TEPCO has long struggled to deal with the growing volume of now contaminated water it has used to cool reactors that went into meltdown after being struck by an earthquake and tsunami in 2011, and the latest find comes as the government has promised to play a greater role in the plant's clean-up.

The discovery of the pipe came a day after Tokyo Electric Power Co (TEPCO) said it found new radiation hotspots at four sites around coolant tanks, with one reading at 1,800 millisieverts per hour -- a dose that would kill a human left exposed to it in four hours.

The pipe, which was found dripping one drop per around 90 seconds and was repaired using adsorption material and plastic tape, accounted for one of the four sites. Water with a radioactivity of 230 millisieverts per hour was found below it, TEPCO said.

Last week the plant operator admitted 300 tonnes of toxic water had seeped out of one of the vast containers -- one of around 1,000 on the site -- before anyone had noticed. The spill sparked fears the toxic water may have seeped into the nearby ocean and was categorised as a Level 3 event, the most serious category since the meltdown itself.

In response to growing domestic and international criticism over TEPCO's handling of the crisis, Japanese Prime Minister Shinzo Abe on Thursday promised the world his government would play a greater role in stopping leaks of highly radioactive water.

"The accident in Fukushima cannot be left entirely to Tokyo Electric Power. There is a need for the government to play a role with a sense of urgency, including taking measures to deal with the waste water," he said.

Abe's pledge came as the world's nuclear watchdog urged Japan to explain more clearly what is happening at Fukushima and avoid sending "confusing messages" about the disaster.